The present invention relates to rotary valves, such as the brake valve employed in railway air brake systems, and more particularly to a method of forming the rotary valve seat.
Generally, a brake valve is activated when the brake valve handle (the operating handle) is placed in the release position. Compressed air is supplied to the brake pipe from the compressed air reservoir. When the brake valve handle is moved to the brake position, the compressed air in the brake pipe is released into the atmosphere and the brake pipe pressure is reduced by the operation of the brake valve.
The valve seat and the rotary valve in the brake valve are in contact (metal-to-metal) and are structured so that the rotary valve rotates on the valve seat when the brake valve handle is operated. There is considerable slide resistance between the rotary valve and the valve seat. Grease is conventionally used between the rotary valve and the valve seat in order to reduce this resistance.
There is, however, just an oil film between the rotary valve and the valve seat. Due to the frequent use of the brake valve handle, the more the brake handle is used, the more the grease is dissipated. Also, the areas where the rotary valve and the valve seat come into contact wear quickly, causing abrasion. The increase in the slide resistance impedes the operation of the handle, and frequent check-ups are required within a short period of time.
Various solutions have been tried to overcome this problem, including teflon coating of the rotary valve seat and the mechanical formation of numerous concavities in the valve seat surface to which a lubricating oil was applied. In the first instance, the teflon coating peeled off with wear and leakage resulted. In the second instance, the surface finish was damaged by the mechanical forming of the concavities in the surface, depending upon the number and location of the concavities, resulting in air leakage.